This invention concerns a process for the manufacture of brown coal briquettes in which pre-dried brown coal is heated and pressed in the heated state.
Many processes for the hot-briquetting of coal are known. The majority of these known processes are in the field of the hot-briquetting of bituminous coal. These known processes are especially useful in the hot-briquetting of stone coal, which possesses a natural bakability. Since brown coal does not have a natural bakability characteristic, the experiences gained from processes found suitable for the hot-briquetting of stone coal cannot be transferred directly to brown coal. In the art of the hot-briquetting of brown coal, several techniques have been known. For example, the German Pat. No. 1,024,921 discloses a process in which, for example, finely diminuted hard brown coal is heated, within 3 to 5 minutes, to a temperature in a range of from about 25.degree. to about 50.degree. C below its "dough point", subsequently one separates up to approximately 40% of the coal and heats this portion, in a few seconds, to a temperature which lies in a range approximately from about 30.degree. to about 50.degree. C over the "dough point". The thus treated portion of the coal is re-combined with the untreated portion, and the combined coal is then briquetted. This method is very expensive.
In another process, known from published German Patent application (DAS) No. 1,671,372, the brown coal is heated, prior to briquetting, to a temperature in the range from about 250.degree. to about 300.degree. C, and then briquetted under high pressure. In this process, however, a supplement of up to about 20% baking stone coal is required to be added to the brown coal in order to obtain briquetttes with compressive strength of over 100 kp/cm.sup.2 which, however, does not meet all requirements. This process was modified, according to the disclosure of published German Patent Application (DAS) No. 1,671,371 in such a way that after the drying of the coal, in an oxygen-free zone, heating of the brown coal takes place at an extremely high rate. For example, in this modified process, 1 minute is recommended as the time period for the heating of the brown coal to a temperature in a range from about 320.degree. to about 350.degree. C.
The known process, as disclosed in the published German Patent application (DAS) No. 1,671,372, has been further modified according to published German Patent application (DAS) No. 1,912,264 in such a manner that after a very quick drying of the brown coal, a preheating of the coal to a temperature in a range of from about 340.degree. to about 420.degree. C and subsequently a further heating, under pressure in a press, to a temperature of approximately 430.degree. C takes place until the tar vapors have completely escaped from the coal. This known process has the disadvantage that the presses, which are in any case subject to wear, require that special heating devices be incorporated therein. In addition, the pressing time must be increased, in order to be able to conduct properly the postheating pressing.
From processes of the type described in the beginning, it can be considered to be generally known that in a carbonization up to the temperatures of approximately 300.degree. C principally only CO.sub.2 and N.sub.2 escape (compare "Braunkohle, Warme und Energie", No. 4, 1971, lines 17-19). Only at temperatures above 300.degree. C is the first formation of tar observed.